How can the best of traditional and modern design and technology be combined to create a carbon neutral home? In the mountains above Kyoto, Japan, one man, (with the help of his friends, family and neighbours), sets out on an intrepid journey to design and build a truly sustainable eco-home. Follow me as I encounter the challenges and solutions that the house and its mountain forest environment present.

A couple of months ago, I posted on the blog about my thoughts on the energy design for the house--a concept based around water and sunlight. I posted these thoughts as a kind of "call-for-advice" on the The Green Building Talk website--a kind of hub for eco architects and design experts.

The forum is not the fastest moving and it took several weeks to get the first responses. But as of today, several experts have responded and the key features of the design are being discussed and decided upon. Please do follow the discussion on the site and chip-in if you have comments/ideas!

[for future-proofing purposes I have pasted a snap-shot of the discussion below...]

original post by me

Learning so much from reading the posts on this site and have got to the point where I simply must get members' comments on the energy design of own developing project design. Many thanks in advance for any advice/feedback! The location is in the Japanese mountains near Kyoto. Being in the mountains means we are cooler than Kyoto city below but this still equates to humid summers with occasional highs in the low 90s. The winters are cold and dry being at attitude with lows in the low 20s in Dec/Jan/Feb with occasional, mostly light, snowfall. I am looking for an energy design solution based around shifting water as the thermal mass and the goal is to keep the solution as cheap and simple as possible. The current house design has lots of glazing on the south side (maybe even over 25% of the total house--the roof slopes up to the south). The 1st floor is around 1200sqf with 550 sqf or so above in a limited second floor configuration. I want to utilize the south facing glazing to warm inside waterwalls/tanks and maybe some kind of inside waterfall that runs to tank/s that release the thermal mass stored overnight (flowing water inside would also help to humidify in the dry winter). I also have a couple of flat-plate collectors that can supplement the heating of indoor tanks/walls (and can buy 1-2 more) and unlimited free firewood for a wood stove (that could have tanks beside or near it). Thinking that one of the tanks will be a solar-fed electric boiler for backup hot water in winter. In the summer I would like to use the collectors for the majority/all of the hot water so perhaps the simplest thing to do would be to use the same electric boiler and insulate it, although this would add an unwanted internal heat source. I was also thinking of a simple backup tankless electric for summer use, fed from a separate outdoor solar storage tank (season switchable). The inside tanks/waterwalls would be emptied in summer and I would either purchase a dehumidifier or use dehumidifying salts in some capacity. A whole-house fan in the roof and vent/feeds in/from the north facing wall/floor/ground would complete the cooling. How does this design strike all you experts out there? What problems will I have in making this work? What are the limitations and can anyone help me calculate insulation needs, water quantities and the like? Also, any ideas on developing the waterfall concept? I like inside running water and it would kind of show-off the energy system at work behind the scenes. Again, any help greatly appreciated!

reply from ecoarchitect

the whole house fan or what we call 'STACK VENTILATION' - inducing air flow by convection sounds really very good.

most of our projects have been between latitudes 36 and 40 degrees north a bit further north than Kyoto.

I am somewhat skeptical of the waterwall ideas and my first impression is to direct you FIRST to a hot water domestic solar panel connected to storage tank and last to an electric on demand water heater. heating the inlet water temperature by solar via a storage tank will work well - you are not that cold of a location.

reply from BadgerBoilerMN

Whole house fans are obsolete, making noise and burning power at once. With 90 degrees and 90% humid, outdoor air blowing air around will not cut it. The Japanese know a bit about HVAC engineering. In fact the mini-splits are one of my favorite tools and have a Mitsubishi heat pump supplementing my own radiant floors. It heats (if I want it to) it cools the air at 25 SEER and dehumidifies without noise or great expense.

I invested insulation, windows and radiant floors but humidity control is a comfort factor you mustn't overlook.

An ERV would be useful to control humidity summer and winter for comfort and building health.

When the weather is perfect (temperature and humidity) nothing beats an open window.
MA
www.badgerboilerservice.com

reply from Dana1

What MA said- in humid summer locations with cool nights a whole-house fan can take down the temperature indoors, but it raises the humidity (sometimes to mold and fungus growing levels.) I's FAR better from both a comfort and energy use point of view to build it air tight and to decent insulation level and actively ventilate with an ERV, controlling humidity with a dehumidifier.

Lots of glazing for high passive solar gain can be the wrong approach in places where it's 90F in the summer. High insulation values, air tight construction, and more moderate (but still substantial) south facing glazing can work, especially if you use seasonal exterior shading to reduce the gain in summer/fall. With air-tight construction and heat-recovery ventilation you won't have wintertime dryness issues, since the humidity can be raised by lowering the ventilation rate. The average temperature in Kyoto in January is about + 5C/40F, so even if you're 1000 meters above the city you don't have "arctic dry" air even in the ventilation stream, and if you used an ERV rather than HRV for the heat recovery you would also be recovering a decent fraction of the humidity (just as it would conserve dehumidification power in summer.)

I'm not sure if they have the weather data for relevant locations in Japan, but the PassiveHouse Institute (see http://www.passiv.de/07_eng/haupt_e.html )has done a GREAT job of modeling heat & humidity in air tight construction for Europe and North America. Their tools are not expensive, and worth using on any new design where you're looking to minimize heating & cooling energy use. You may still get good results with the tools if you use a location elsewhere with a similar climate and latitude.

reply from me

Many thanks for all the advice! So, at the moment I am looking at solar-collectors->-storage tank->-electric point-of-use-water heaters->-hot water. [Question: is there a way I can add radiant floors with a simple kit running from the storage tank (perhaps even a electric point of use heater that is designed for the purpose?)]

Cutting down slightly on the south-facing glazing, planting some trees on the south side for seasonal shading. Air tight construction, good insulation, ERV and mini-splits (supplemental heating and dehumidifying) for different zones.

On the storage tank issue: I was wondering how well a section of a natural swimming pool (along a "hot tub" principle) would work as a "store". I am getting very cheap 2nd hand solar collectors here and was considering putting 10 or so of them on the property and feeding them into a semi-separate"hot tub" section of a south facing natural swimming pool. I would then take water from the top layer of this store--which would be covered with an insulating lid in winter--through a UV sanitizer direct to the point-of-use on demand electric heaters.